Hi Andrea. When the client disconnects, and your servlet tries to write to the output stream, Tomcat will throw a ClientAbortException (you may have already seen this):
http://tomcat.apache.org/tomcat-6.0-doc/api/org/apache/catalina/connector/ClientAbortException.html Tomcat appears to only throw this exception when you either write some bytes to the output stream or when you flush the output stream, and the client already closed its end of the connection. It appears that you could periodically try flushing the output stream and see if doing so throws this exception. You can flush after writing any number of bytes, including zero bytes. The first time you call flush, it will send the HTTP response headers to the client, so you would need to first set the headers before flushing. That sounds difficult for you to do because you're writing an image, and one of the headers would be Content-Length, which you probably don't know until your image is generated. -- Jason Brittain On Mon, Sep 28, 2009 at 12:21 AM, aaime74 <andrea.a...@gmail.com> wrote: > > Hi, > I'm working on the development of an open source application, GeoServer, > implementing the Web Map Service specification. > The specification allows a client to request maps using simple GET > requests like: > > > http://sigma.openplans.org:8080/geoserver/wms?WIDTH=431&SRS=EPSG%3A4326&LAYERS=tiger-ny&HEIGHT=550&STYLES=&FORMAT=image%2Fpng&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetMap&EXCEPTIONS=application%2Fvnd.ogc.se_inimage&BBOX=-74.01697805908182,40.69808217724622,-73.99567744140603,40.72526393994153 > > and the client gets back a PNG with a map of the request area. > No asynchronism is allowed, the protocol is standardized > (http://portal.opengeospatial.org/files/?artifact_id=1058) and I have no > controls over the clients (there are tens of them around, both open source > and proprietary) which are free to make as many request as they like, in > whatever order the like. > > By spec we're forced to use a plain request and response approach, but > we're experiencing a problem with clients making lots of request as the > user zooms/pans around: basically a request is made, but the user keeps > on moving, the client drops the older requests (closing the connection in > face of > the server) and makes others. > Unfortunately in the meantime the older requests are still running, drawing > a map takes > time and a lot of memory, for example the above request, which is a > small one btw, allocates a BufferedImage of 700KB. The memory is > consumed up until the image is encoded out to the stream, which is also > the moment we finally figure out the client dropped the connection > (since writing to the servlet output stream fails). > > This is very sub-optimal. Servers like Apache with cgi do kill the cgi > process the moment the connection is dropped, significantly reducing the > server load both in terms of CPU and memory consumption. > > Is there any way to check if the client connection is still open using > only the standard servlet API? > If not, is there any Tomcat specific approach that might work instead? > > If there is no solution that can be applied at the general servlet > api level, do you know of any Tomcat specific approach one could use? > e.g., casting the HttpServletResponse to some Tomcat specific class > and get some connection information status there? > > Cheers > Andrea > -- > View this message in context: > http://www.nabble.com/How-to-check-if-the-client-dropped-the-connection-tp25641481p25641481.html > Sent from the Tomcat - User mailing list archive at Nabble.com. > > > --------------------------------------------------------------------- > To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org > For additional commands, e-mail: users-h...@tomcat.apache.org > > -- Jason Brittain
